1. Field of the Invention
The present invention relates to a canister device for use in a gasoline tank.
2. Description of the Prior Art
Known evaporation control systems for limiting the discharge of fuel vapors generated in a fuel tank of a vehicle have been disclosed in the specification of, for example, Japanese Utility Model Laid-Open No. 123953/1982 and U.S. Pat. No. 3,884,204.
In the system disclosed in Japanese Utility Model Laid-Open No. 123953/1982, the fuel vapors evaporated into a vapor space of a fuel tank from gasoline stored in the fuel tank are collected, while the engine is stopped, in a fuel vapor absorbing canister (hereinafter referred to simply as a canister) by a vent conduit through a check valve therein, and are absorbed by and stored in an active vapor absorbing material, such as activated carbon, filling in the canister.
While the engine is operating, a source of vacuum generated in an intake manifold is utilized to remove the accumulated fuel vapors from the vapor absorbing material in the canister and draw them into the intake manifold by a purge conduit for consumption in the engine combustion process.
This system, however, is not equipped with means for collecting the fuel vapors evaporated into a filler neck of the gasoline tank from the gasoline which is being filled into the tank, and is therefore not suitable for conforming with the recent tendency of restricting the discharge of fuel vapors into the atmosphere to avoid air pollution.
The vapor loss control system disclosed in U.S. Pat. No. 3,884,204 includes a first canister in which the fuel vapors generated in a vapor space in the gasoline tank are collected by a first vent conduit, and a second canister in which the fuel vapors generated in a filler neck of the fuel tank while the tank is being filled are accumulated by a second intake conduit. The canisters are purged when the engine is running by utilizing the vacuum source generated in the intake manifold to remove the vapors therefrom and draw them into the intake manifold through purge conduits provided for the respective canisters.
This system, however, has a disadvantage in that the number of steps required for assembly and the number of parts are increased because a pair of canisters are used, increasing the production cost.
In the system disclosed in the specification of Japanese Utility Model Laid-Open No. 123953/1982, the fuel vapors generated from the fuel tank and a carburetor bowl are collected in one canister by two separate intake conduits, and the absorbed fuel vapors are purged from the canister to the intake manifold through a purge conduit. The above-described problem of the prior art is obviated if the canister of the above system is used to collect, by separate intake conduits, fuel vapors generated in the vapor space in the gasoline tank and fuel vapors generated in the filler neck of the fuel tank. The canister of this arrangement generally communicates with two intake conduites at one end surface thereof, but this arrangement produces the following problem: the temperature of the gasoline stored in the fuel tank is higher than that of the gasoline to be poured into the tank. As a result, the fuel vapors collected in the vapor space in the gasoline tank contains a large amount of high-boiling components, while the fuel vapors evaporated into the interior of the filler neck of the fuel tank from the gasoline which is being poured into the tank while the tank is being filled contains a large amount of low-boiling components. The activated carbon which fills the canister as an active vapor absorbing material has characteristics such that it does not readily release the high-boiling components of the absorbed gasoline, reducing the absorption efficiency thereof. Therefore, if the fuel vapors evaporated from the gasoline stored in the gasoline tank are collected in the canister from one end surface thereof and are absorbed in the active vapor absorbing material consisting of activated carbon, the large amount of high-boiling components contained in the fuel vapors spread all over the active vapor absorbing material, reducing the absorption efficiency of the material at an early stage of its use and also deteriorating the function of the canister.